PARTIENDO DE UNA OBSERVACION EN EL CUMULO DE COMA AFECTUADA POR EL SATELITE EXOSAT DURANTE SU FASE DE VERIFICACION DE CARACTERISTICAS SE PUDO OBSERVAR LA GRAN DENSIDAD DE FUENTES DE RAYOS X DESCONOCIDA EN ESE CAMPO. A PARTIR DE ESTOS RESULTADOS PREVIOS SE OBTUVO TIEMPO PARA EFECTUAR OTRA OBSERVACION MAS LARGA EN LA MISMA REGION EN 1985. EL ANALISIS

This thesis has been dedicated to the study of Galaxy Clusters as Cosmological tools. The work is divided into two main parts; the first is purely observational, whereas the second is dedicated to the preparation of tools for cosmological analyses. The observational section has been developed within the frame of the optical validation program

Not Available Based on observations collected at the European Southern Observatory.

Over 2,000 stars were observed for one month with a high enough cadence in order to look for acoustic modes during the survey phase of the Kepler mission. Solar-like oscillations have been detected in about 540 stars. The question of why no oscillations were detected in the remaining stars is still open. Previous works explained the non-detection

Aiming to extract cosmological information from linear scales of the WISE×SuperCOSMOS photometric redshift catalog, we perform a characterization of the systematic effects associated with stellar content, evidencing the presence of contamination and obscuration. We create an integrated model for these effects (which together we call "usurper